Sintering



United States Patent SINTERING Kurt Meyer, Frankfurt am Main, and Hans Rausch,

Oberursel (Taunus), Germany, assignors toMetallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany No Drawing. Application July 10, 1956 I Serial No. 596,832

2 Claims. (Cl. 75--5) This invention relates to a process and apparatus for the sintering of materials. In particular, the invention is directed to a novel method of sintering fine-grained ores, especially iron ores.

In the making of large pellets from dust or fine-grained materials, as by pelletizing or agglomerating of granulating the fine-grained materials, certain eificiencies of procedure have been found as disclosed in the copending application of Meyer et al., S. N. 604,525, filed 16 August 1956.

The heretofore suggested methods of agglomerating and thus forming coherent lumps from fine-grained materials are tabulated into two processes. First, the moistened fine-grained materials are mixed as uniformly as possible with fuel and on occasion with return material in mixing apparatus such as for example in Eirich mixers, mixing drums, or cutting screw conveyors. This so called crumbled material is deposited without any further treatment upon a sintering band, whereupon it is heat treated to form a coherent sinter cake, which is broken up and fed to a blast furnace. The output of this process, with oxidic iron ores, amounts to from 17 to 19 tons per 24-hour day per square metre.

A second process lies in taking finely ground ores and pelletizing the same either alone or mixed with inert, recycled sintered material, or with fuel by rolling the mixtures in granulators, such as a plate granulator or granulating drum. An output of particles of substantially uniform size is obtained which is placed upon a sintering band for further processing. The granular size of this aforesaid process is between 20 and 30 mm. with a tolerance of plus or minus from 1 to 2 mm.

The output of this process can be screened in order to obtain particles of uniform size if desired, although a properly maintained apparatus produces an output which does not need screening. In this second process, the sintered material is composed of individual pellets which do not stick to each other. In the preparation of oxidic iron ores, the output of the sinter belt amounts to from to tons per 24-hour day per square meter.

According to this invention, the output of the sintering apparatus can be considerably increased if the crumbled mixture formed according to the first-mentioned process is given a further treatment by afterpelletizing, granulating, or agglomerating it in a rolling or giranulating drum prior to being placed upon the sintering band. By so doing, the output of the sintering apparatus rises to 25 to tons per 24-hour day per square metre, and the sintered material takes the form of a coherent cake according to the first-mentioned process, rather than in the form of individual pellets as obtained in the second-mentioned process.

In practice, it has been found that the formation of large pellets is not necessary. Pellets of from 2 to 10 mm. are quite sufiicient. Moreover, it has been found that it is not necessary to form a sinter bed of uniform particle size. The increased output of this invention is obtained with. pellets, the

majorityt ofx which have a granular size between 2 and 10 mm.

7 It is preferable to place thepellets on the sintering band immediately, upon their. formation, inasmuch ast-hey are very, mechanically sensitive, and afterivformationt should be maintained in green-pellet form as short a time: as

1 possible.

. It is also advantageoustto control therate of formation of the green pelletsingaccordance with/the demand of the sinter band so that there is no oyerproduction of the green pellets.

An example of the 'inventionqis'as, follows:

. Pellets are formed of alimy minette, siliceouszminette and blast furnace dust having the following sieve and ignition loss, weight and wetness analysis:

Grain size, mm.: Blast furnace dust portion in percent 0.5-1 1.5 0.2-0.5 14.5 0.1-0.2 66.5 0.09-0.1 8.0 0.06-0.09 7.0 0.00-0.06 2.5

Blast Limy siliceous Furnace Minette Minette Dust Poured Weight, kg./l.=Liter 1. 2 1.80 1. 4 Wetness at time of supply, percent- 10.0 16. 0 gnition Loss, percent 16. 4 25. 6 16. 3

Limy siliceous Ore Mixture Grain Size, mm. Minette Minette Portion in Portion in Portion in percent;

percent percent Treated Ore Mixture In Example 1, the above-entitled material was pelletized on a countercurrent, high speed mixer with the addition of coke and recycled material plus water. The pelletized material was placed on a grate of -40 x 40 cm., and gas was drawn through the material by suction boxes at 700 mm. water column. The maximum exhaust gas temperature was 280 C. The average waste gas quantity was operational m. /m /min., and the hot discharge sintering time was 13:50 minutes. This hot discharge amounted to an output of 19 tons/day/m. The residual coke fraction was 7% relative to the ore carrier.

A second example comprises a two-step operation, with a one-step pre-mixing of the fine material and a subsequent granulation.

The same ingredients as given in the first aforesaid process were used, but the pellets formed were given a second treatment by being rolled in a drum for five minutes at 18 R. P. M. The drum had a length of 1.8 m. and a diameter of 1.0 m.

A sinter bed of about 30 cm. thickness was formed on the sinter belt. A vacuum of 600 mm. water column was pulled through the bed, and a maximum exhaust gas temperature of 300 C. was obtained.

The average exhaust waste gas quantity was 75 operational mfi/mP/min. The material was sintered for 10:30 minutes. The hot discharge output of the bed was 25 tons/day/mfi, and the coke fraction was 7% relative to the ore carrier.

A comparison of the above two methods shows that the second two-step method produces an increase of 31% of the output of the sintering apparatus. In each case, the quality of the sintered product is substantially the same.

Having now described the means by which the objects of the invention are obtained, we claim:

1. A process for sintering fine grained oxides of metals which are subsequently reduced, comprising mixing and crumbling a moist mixture of said oxides, sintered re- 5 turn material and solid fuel, said fuel being in a quantity to leave a substantial amount of residual coke within the sintered product, rolling the crumbled mixture to form pellets of non-uniform size ranging in diameter from 2 to 15 mm., and immediately thereafter sintering a mass of said pellets to form a coherent sinter cake adapted to be broken up for further processing.

2. A process as in claim 1, said pellets being composed of limy minette, siliceous minette, blast furnace dust, and fuel.

References Cited in the file of this patent UNITED STATES PATENTS Lellep June 12, 1956 FOREIGN PATENTS Great Britain Apr. 22, 1953 

1. A PROCESS FOR SINSTERING FINE GRAINED OXIDES OF METALS WHICH ARE SUBSEQUENTLY REDUCED, COMPRISING MIXING AND CRUMBLING A MOIST MIXTURE OF SAID OXIDES, SINTERED RETURN MATERIAL AND SOLID FUEL, SAID FUEL BEING IN A QUANTITY TO LEAVE A SUBSTANTIAL AMOUNT OF RESIDUAL COKE WITHIN THE SINTERED PRODUCT, ROLLING THE CRUMBLED MIXTURE TO FORM PELLETS OF NON-UNIFORM SIZE RANGING IN DIAMETER FROM 2 TO 15 MM., AND IMMEDIATELY THEREAFTER SINTERING A MASS OF SAID PELLETS TO FORM A COHERENT SINTER CAKE ADAPTED TO BE BROKEN UP FOR FURTHER PROCESSING. 